Pulse stimulation tool and method of use

ABSTRACT

A downhole pulse stimulation tool for use within a production or injection string including a tubing string, a rotating or reciprocating rod string and a downhole pump. The tool is formed by a resonance chamber defined by a cylindrical outer tubular member connected to the tubing string and having pulse emitting openings, a pulse generator rotatably disposed within the resonance chamber having longitudinal channels and defining pulse generating openings, wherein the pulse generating openings periodically align with the pulse emitting openings as the pulse generator rotates or reciprocates within the resonance chamber.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the priority benefit of U.S. Provisional Patent Application No. 61/169,931 filed on Apr. 16, 2009 entitled “Pulse Stimulation tool and Method of Use”, the contents of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a pulse stimulation tool for downhole application and their use to enhance production of oil and gas wells.

BACKGROUND OF THE INVENTION

Within a petroleum producing well, the production string forms the primary conduit through which production fluids (liquids, gases, or any fluid produced from a wellbore) are produced to the surface. The production string is typically assembled with production tubing and completion components in a configuration that suits the wellbore conditions and the production method. Oil and gas wells typically vary from a few hundred to several thousand feet in depth, and there is often insufficient formation pressure to cause the flow of production fluids through the production string to the surface.

Several prior art systems involving different pumping and extraction devices have been developed for the surface transfer of production fluids from a well. Downhole hydraulic pumps installed deep within the well are commonly used. A surface hydraulic pump pressurizes power oil which drives the downhole pump. When a single production string is used, the power oil is pumped down the tubing and a mixture of the formation crude oil and power oil are produced through the annulus between the casing and the tubing. If two adjacent production strings are used, the power oil is pumped through one of the pipes, and the mixture of formation crude oil and power oil are produced in the other, parallel pipe.

Prior art artificial lift systems include for example, the progressive cavity pump and plunger lift, both of which may be installed on jointed or continuous rods; electric submersible pumps (ESPs); gear pumps which may be installed on tubing and powered by downhole electric or hydraulic motors; and venturi lift pumps which are run on coiled tubing but is not a total production system.

It is known that pressure pulses can enhance the flow rate of fluids and mixtures of fluids and solids from producing formations, therefore, there is a need in the art for downhole apparatuses which can produce pressure pulses in order to enhance production rates.

SUMMARY OF THE INVENTION

The present invention is directed to a downhole pulse stimulation tool. In one aspect, the invention may comprise a tool for use within a production or injection string including a tubing string, a rod string and a downhole pump, the tool comprising:

(a) a resonance chamber defined by a cylindrical outer tubular member defining at least one pulse emitting opening, the outer tubular member connecting to the tubing string;

(b) a pulse generator rotatably disposed within the resonance chamber, the pulse generator having a longitudinal channel and defining a least one pulse generating opening, wherein the at least one pulse generating opening periodically aligns with the pulse emitting opening as the pulse generator rotates with the resonance chamber to provide fluid communication from the longitudinal channel to outside the outer tubular member;

(c) wherein the pulse generator is directly or indirectly rotated by the rod string.

In another aspect, the invention may comprise a downhole pulse stimulation tool for use within a production or injection string including a tubing string, a reciprocating rod string and downhole pump, the tool comprising:

(a) a resonance chamber defined by a cylindrical outer tubular member defining at least one pulse emitting opening, the outer tubular member connecting to the tubing string;

(b) a pulse generator slidingly disposed within the resonance chamber, the pulse generator having a central bore and defining a least one pulse generating opening, wherein the at least one pulse generating opening periodically aligns with the pulse emitting opening as the pulse generator reciprocates with the resonance chamber to provide fluid communication between the central bore and the exterior of the outer tubular member;

(c) wherein the pulse generator is directly or indirectly reciprocated by the rod string.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described by way of an exemplary embodiment with reference to the accompanying simplified, diagrammatic, not-to-scale drawings.

FIG. 1 is a schematic view of a pump system incorporating one embodiment of the present invention.

FIG. 2A is a cage line view of one embodiment of the invention.

FIG. 2B is a side view;

FIG. 2C is a cross-sectional view along line A-A of FIG. 2B;

FIG. 2D is an end view; and

FIG. 2E is a detail view of FIG. 2D.

FIG. 2F shows a longitudinal cross-section of one embodiment of the invention.

FIG. 3 is a schematic representation of a dual pump system, where a lower inverted pump drives a pressure emitting tool at the bottom of the tool string.

FIG. 4A is a cage line view of one embodiment having a cruciform slot channel pattern, which may be used below an inverted pump.

FIG. 4B is a longitudinal cross-sectional view of this embodiment.

FIG. 5 is a diagrammatic representation of a pulse generator having helical channels.

FIG. 6A is a cage line view of one embodiment showing helical channels in a pulse generator.

FIG. 6B is a longitudinal cross-sectional view of FIG. 6A.

FIG. 7 is a schematic view of the embodiment of FIGS. 5 and 6 in an injection well.

FIG. 8 is a cross-sectional view of one embodiment, adapted for use with a reciprocating rod string and pump.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides for a downhole pulse stimulation tool. When describing the present invention, all terms not defined herein have their common art-recognized meanings. To the extent that the following description is of a specific embodiment or a particular use of the invention, it is intended to be illustrative only, and not limiting of the claimed invention. The following description is intended to cover all alternatives, modifications and equivalents that are included in the spirit and scope of the invention, as defined in the appended claims.

“Horizontal” means a plane that is substantially parallel to the plane of the horizon. “Vertical” means a plane that is perpendicular to the horizontal plane. One skilled in the art will recognize that wellbores may not be strictly vertical or horizontal, and may be slanted or curved in various configurations. As used herein, the term “longtudinal” means aligned with the axis of the wellbore, while “transverse” means a plane which is substantially perpendicular or at an angle to the longitudinal axis.

In one embodiment, the invention comprises a downhole pulse stimulation tool for use within a production string including a tubing string (T), a rod string (R) and a downhole pump (P). In this embodiment, the tool is placed above the pump. Embodiments of the tool may be adapted for use with a progressive cavity pump, a reciprocating pump, an electric submersible pump, or other artificial lift solutions.

The tool (10) comprises a resonance chamber (12) and a pulse generator (14). The resonance chamber (12) comprises a housing which forms part of the tubing string (T) and defines at least one pulse emitting opening (16). The pulse generator (14) is disposed within the tubing string (T) and moves within the resonance chamber (12). The pulse generator (14) defines at least one pulse generating opening (18) which periodically aligns with the pulse emitting opening (16) as the pulse generator moves within the resonance chamber (12) housing.

In one embodiment, shown in FIGS. 2A-2E, the resonance chamber is defined by a hollow cylindrical outer tubular member (12) which defines a pair of pulse emitting openings (16), disposed opposite each other. The pulse generator (14) comprises a generally cylindrical member which fits within the resonance chamber (12) and rotates within the resonance chamber. In one embodiment, the inner profile of the resonance chamber may define a seat (20) which may be tapered, which retains the pulse generator. The pulse generator may also have an outside taper which may match the inside taper of the pulse generator (14), as shown in FIG. 2C. If used, the seat (20) prevents downward movement of the pulse generator within the resonance chamber. Alternatively, the inner profile of the resonance chamber and the outer profile of the pulse generator may be straight and parallel the longtudinal axis of the outer tubular member (12).

As shown in FIG. 2D, the pulse generator (14) defines a plurality of longitudinal channels (22), substantially parallel to, and arrayed around, the axis of rotation. The pulse generating opening (18) opens into one of the longitudinal channels (22). In one embodiment, the pulse generator is installed in a progressive cavity pump system, and is directly attached to a rotating rod string, preferably by a threaded attachedment. An actuator (not shown) attaches below the pulse generator and attaches to a pump rotor. Thus the rod string rotatingly drives both the pulse generator and the pump rotor at the same speed.

As the pump (P) is rotated, fluid is displaced upward into the tubing string (T) through the pulse generator. The pumped fluid passes through the longitudinal channels, at the same time the pulse generator rotates within the resonance chamber. The pulse generating opening (18) periodically aligns with the pulse emitting opening (16) as the pulse generator rotates. The fluid within the pulse generator is at a higher pressure than outside the tubing string due to the pump action. As a result, a pulse of fluid pressure is emitted outward from the resonance chamber and into the fluid in the annular space surrounding the tubing string. The frequence of the pulses depends on the number of pulse generating and emitting openings, and the speed of rotation of the pulse generator. The amplitude of the pulses depends on the pressure differential between the pressure within the tubing string, and in the formation.

In one embodiment, there are multiple longitudinal channels, at least one of which defines a pulse generating opening. If there are two pulse emitting openings in the resonance chamber, two pressure pulses will be emitted every rotation of the pulse generator. In one embodiment, there are five longitudinal channels, with one pulse generating opening, and two pulse emitting openings.

The pulse generator may be directly connected to the rod string by a threaded connection to a central connection. Alternatively, an adaptor or other suitable connection mechanism can be used in an indirect connection.

In an alternative embodiment, schematically illustrated in FIG. 3, the pulse stimulation tool (100) is placed below the pump (P). A slotted sub (110) is attached below the pump and provides a fluid intake for the pump as well as the tool (100). A secondary pump (112) is inverted below the slotted sub (110) and pumps fluid downward into the tool (100). The pulse generator (114) rotates within the resonance chamber (116) housing (117) by means of rod (102), which is driven by an extension of the main pump (P). In one embodiment, the pulse generator (114) defines channels which are elongate slots (118) arranged in a cruciform pattern, as shown in FIG. 4. At least one, and preferably all four of the channels (118) defines a pulse generating opening (120), and the resonance chamber housing (117) defines at least one, and preferably four pulse emitting openings (122), positioned equidistant around the periphery of the resonance chamber. Thus, in one embodiment, a pressure pulse is simultaneously emitted from all four openings every 90° rotation of the pulse generator.

In one embodiment, a secondary outlet is formed by a bottom plate (124)) which has a cruciform slot pattern (126) which matches the channel (118) pattern in the pulse generator and also defines at least one secondary pulse emitting openings (128) which open downwards through the bottom plate. Alternatively, the secondary openings (128) may open laterally. The secondary outlet bottom plate (124) may be then mounted stationary and flush against the bottom of the pulse generator, oriented such that the cruciform slots (126) align when the pulse emitting and generating openings are aligned. Thus, pressure from the resonance chamber is pulsed periodically from the pulse emitting openings (122) and from the secondary openings (128) simultaneously. As shown in FIG. 3, pressure pulses are thereby fired sideways and downward into the formation.

In another alternative embodiment, the pulse generator is not directly rotated by the rod string or pump, but rather is rotated by the movement of fluid through the pulse generator. The pulse generator (210) rotates on an axle (212) within the resonance chamber housing (201).

In one example, shown schematically in FIGS. 5 and 6A and 6B, longitudinal channels (214) are curved within the pulse generator, such that fluid which passes through the pulse generator under pressure, causes rotation of the pulse generator about axle (212). In one embodiment, the curved channels (214) are helically disposed about the axis of rotation. At least one of the curved channels has a pulse generating opening (216). In one embodiment, the pulse generator defines an upper pulse generating opening (216A) and a lower pulse generating opening (216B), and preferably both the upper and lower pulse generating openings open into the same helical channel (214).

The pitch of the helical channels may be varied. In one embodiment, each channel makes at least one rotation within the pulse generator. If upper and lower pulse generating openings are provided, the two openings may then be substantially aligned longitudinally on the resonance chamber housing (201).

The resonance chamber may define at least one pair of upper and lower pulse emitting openings (218), and preferably two pairs of pulse emitting openings (218) are provided, as shown in FIG. 6. As will be appreciated by those skilled in the art, if one pair of pulse generating openings (216) are provided, which periodically align with two pairs of pulse emitting openings (218), then each rotation of the pulse generator (210) will generate two sequential pulses, each pulse comprising a simultaneous pulse from each of the upper and lower openings (218).

In one embodiment, the helical pulse generator (210) may be deployed below a progressive cavity pump or an electric submersible pump, but above the pump intake. The pulse generator will be rotated by the fluid being sucked into the pump. The amplitude of the pulses emitted may be smaller due to the reduced fluid pressure caused by the pump suction.

In one embodiment, the helical pulse generator (210) may be deployed within a injection well, as shown schematically in FIG. 7. The injection fluid (IF) will create the rotational motion of the pulse generator as it passes through the device, and will generate periodic fluid pressure pulses as described above. A small portion of the injection fluid will thus escape through the pulse emitting openings (218) out into the annular space in the injection well.

Embodiments of the present invention may also be adapted for use with a reciprocating rod string and downhole pump. Reciprocating downhole pumps are conventional and well-known in the industry.

In one embodiment, the tool (300) may comprise a resonance chamber (312) defined by a cylindrical outer tubular member (301) defining at least one pulse emitting opening (302), the outer tubular member (301) connecting to the tubing string as described above. Preferably, there are four pulse emitting openings, each on the same transverse plane, and positioned equidistant about the periphery of the resonance chamber (312).

The pulse generator (310) is slidingly disposed within the resonance chamber and is attached the rod string by means of a rod connector (303), which has a number of openings permitting fluid flow upwards into the tubing string. The pulse generator (310) defines a number of pulse generating openings (314). In one embodiment, the number of pulse generating openings (314) matches the number of pulse emitting openings (302), and are longitudinally aligned with the pulse emitting opening(s). Therefore, as the pulse generator (310) reciprocates with the rod string, the pulse generating openings (314) periodically align in the same transverse plane with the pulse emitting openings (302), once on the upstroke and once on the downstroke. As will be appreciated by those skilled in the art, the upstroke pressure pulse will be stronger than the downstroke pulse, because of the higher pressure differential caused by the upstroke.

In one embodiment, the production of fluids may be enhanced by the use of chemical additives injected downhole.

As will be apparent to those skilled in the art, various modifications, adaptations and variations of the foregoing specific disclosure can be made without departing from the scope of the invention claimed herein. 

1. A downhole pulse stimulation tool for use within a production or injection string including a tubing string, a rotating rod string and a downhole pump, the tool comprising: (a) a resonance chamber defined by a cylindrical outer tubular member defining at least one pulse emitting opening, the outer tubular member connecting to the tubing string; (b) a pulse generator rotatably disposed within the resonance chamber, the pulse generator having a longitudinal channel and defining a least one pulse generating opening, wherein the at least one pulse generating opening periodically aligns with the pulse emitting opening as the pulse generator rotates with the resonance chamber to provide fluid communication from the longitudinal channel to outside the outer tubular member; (c) wherein the pulse generator is directly or indirectly rotated by the rod string.
 2. The tool of claim 1 wherein the pulse generator defines at least two longitudinal channels, substantially parallel to the axis of rotation, wherein the at least one pulse generating opening opens into one of the longitudinal channels.
 3. The tool of claim 2 wherein the pulse generator defines five or more longitudinal channels.
 4. The tool of claim 2 wherein the pulse generator is directly rotated by the rod string.
 5. The tool of claim 1 wherein the pulse generator comprises a plurality of curved channels, wherein fluid flow through the curved channels causes rotation of the pulse generator.
 6. The tool of claim 5 wherein the plurality of curved channels are helically disposed about the axis of rotation.
 7. The tool of claim 6 wherein the pulse generator defines an upper pulse generating opening and a lower pulse generating opening, wherein both the upper and lower pulse generating openings open into the same helical channel.
 8. The tool of claim 6 wherein the plurality of helical channels make substantially one or more rotations about the axis of rotation.
 9. The tool of claim 2 wherein the longitudinal channels comprise slots extending radially outward from a central portion to a periphery of the pulse generator.
 10. The tool of claim 9 wherein the slots are configured in a cruciform configuration.
 11. The tool of claim 9 further comprising a secondary outlet comprising a bottom plate defining openings which come into and out of alignment with the slots as the pulse generator rotates.
 12. A downhole pulse stimulation tool for use within a production or injection string including a tubing string, a reciprocating rod string and downhole pump, the tool comprising: (a) a resonance chamber defined by a cylindrical outer tubular member defining at least one pulse emitting opening, the outer tubular member connecting to the tubing string; (b) a pulse generator slidingly disposed within the resonance chamber, the pulse generator having a central bore and defining a least one pulse generating opening, wherein the at least one pulse generating opening periodically aligns with the pulse emitting opening as the pulse generator reciprocates with the resonance chamber to provide fluid communication between the central bore and the exterior of the outer tubular member; (c) wherein the pulse generator is directly or indirectly reciprocated by the rod string. 